This invention relates to a curved-surface printing method applicable to a member exposed to a high-temperature closed atmosphere and a lamp having the method applied thereto, and more particularly to a curved-surface printing method which is effectively applicable to manufacturing of an extension exposed to a high-temperature closed atmosphere while being incorporated into a head lamp of an automobile or the like and a lamp unit to which the method is applied.
A development proceeded in a field of a design of an automobile or the like extends over a variety of parts. For example, such a design development is directed to detail of an extension arranged in a lamp unit of an automobile as well. In order to meet such requirements, it is necessarily required to carry out a coloring treatment as well as a molding treatment on the extension. However, when the extension is formed so as to have a three-dimensional configuration, the coloring treatment is restricted to execution in a relatively simple way. More specifically, the three-dimensional configuration causes the coloring treatment to be limited to coloring by spray coating, reproduction of metal coloring by vacuum deposition, utilization of colors of materials for the extension or the like, to thereby render formation of a pattern on the extension substantially impossible. However, recent diversification of a demand for a design treatment requires that the three-dimensional configuration be provided with a complicated pattern arrangement. More specifically, in an extension for a lamp unit wherein a normal head lamp and a fog lamp are covered with a single lens, a relatively large space is necessarily defined on a portion of the extension between an opening for the head lamp and that for the fog lamp, so that there is increased a demand for applying any desired pattern onto the space, to thereby provide the lamp unit with any added value or distinct properties.
Conventionally, water pressure transfer printing techniques are employed for curved-surface printing on a member formed to have such a three-dimensional configuration. The water pressure transfer printing is carried out in such a manner that a transfer film formed by coating a transfer ink onto a water-soluble film is floated on water in a water tank and then an object to which the transfer ink is to be transferred (hereinafter referred to as xe2x80x9cobjectxe2x80x9d) such as an extension as described above or the like is downwardly pressed against the transfer film, resulting in the transfer ink being transferred to a surface of the object by water pressure. The transfer film has an activator applied thereto before or after it reaches the water, to thereby provide the transfer ink with stickiness.
A lamp unit including a head lamp and the like is heated at an interior thereof to an elevated temperature while being sealedly closed during operation thereof, because a bulb such as a halogen bulb or the like is kept turned on during the operation. Thus, when the curved-surface printing is carried out on an interior member of the lamp unit, a high-temperature closed atmosphere formed in the lamp unit due to the operation causes partial volatilization of the transfer ink and/or activator, leading to a problem of so-called fogging which causes generation of haze in the lamp unit. Essentially, the lamp unit must be designed so as to meet requirements of light distribution provided in a relevant law. Such fogging deteriorates light distribution performance of the lamp unit and a driver""s field of vision.
Such fogging is generally defined in the form of a haze value measured using a direct-reading type haze computer manufactured by SUGA TEST INSTRUMENTS CO., LTD. (a Japanese corporation) according to a glass haze test procedure defined in ISO-6452. The glass haze test is generally carried out in a manner to heat a specimen in a closed vessel to volatilize a volatile ingredient from the specimen and deposit the volatile ingredient onto a glass plate. Then, a glass haze is calculated as a ratio of the amount of light scattered by the glass plate to the total amount of light transmitted through the glass plate. A glass haze of 10% or less measured by the above-described direct-reading type haze computer is determined as a criterion. Thus, a glass haze of 10% or less is used herein as a criterion for indicating that the occurrence of fogging is restrained. Also, a glass haze of 5% or less is judged to be desirable in view of a thickness of a lamp unit, an internal volume of a light emitting section of a bulb, a variation in individual lamp unit products in mass production and the like.
In order to restrain the occurrence of fogging, it would be considered that the extension is formed of a transparent material to have a partition-like shape, the light emitting section is divided into a lens-side space and a reflector-side space and printing on the extension is carried out at a portion of the extension positionally corresponding to the light-emitting section. However, such an approach causes the space for the light emitting section to be reduced, thereby failing to put the lamp unit to practical use. Thus, the prior art fails to permit the lamp unit, in which the extension having the printed pattern formed on a surface thereof is incorporated, to be put to practical use. Arrangement of the pattern is limited to a surface of the lamp unit.
The present invention has been made in view of the foregoing disadvantages of the prior art.
Accordingly, it is an object of the present invention to provide a curved-surface printing method applicable to a member exposed to a high-temperature closed atmosphere which is capable of effectively restraining the occurrence of fogging while ensuring satisfactory curved-surface printing on an extension arranged in a lamp unit or the like.
It is another object of the present invention to provide a lamp unit which is capable of permitting such a curved-surface printing method applicable to a member exposed to a high-temperature closed atmosphere to be effectively applied thereto.
In accordance with one aspect of the present invention, a curved-surface printing method is provided which is applicable to a member exposed to a high-temperature closed atmosphere. The curved-surface printing method includes the step of floating a transfer film on water in a water tank. The transfer film is formed by coating a transfer ink on a water-soluble film. The curved-surface printing method also includes the steps of downwardly pressing an object against the transfer film to print the transfer ink on a surface of the object by water pressure, providing the transfer film with stickiness sufficient to ensure transfer of the transfer ink to the object by means of an activator which contains a plasticizer ingredient selected from the group consisting of dimethyl phthalate (DMP) and diethyl phthalate (DEP), and carrying out a volatilization promoting drying treatment for substantially volatilizing the plasticizer ingredient after transfer of the transfer ink to the object.
In a preferred embodiment of the present invention, the curved-surface printing method further includes the step of draining the object of which a surface is still wet prior to the volatilization promoting drying treatment.
In a preferred embodiment of the present invention, the volatilization promoting drying treatment is carried out for about 30 to 60 minutes at a temperature of about 120xc2x0 C.
In a preferred embodiment of the present invention, the draining step is carried out for about 15 minutes at a temperature of about 80xc2x0 C.
In a preferred embodiment of the present invention, the draining step and volatilization promoting drying treatment are carried out in a single stage by adjusting a drying temperature and drying time.
In a preferred embodiment of the present invention, the curved-surface printing method further includes the step of subjecting the object to undercoating prior to the transfer printing of the transfer ink on the surface of the object.
In a preferred embodiment of the present invention, the object exhibits fogging of 10% or less in a glass haze test.
In a preferred embodiment of the present invention, the object exhibits fogging of 5% or less in a glass haze test.
In a preferred embodiment of the present invention, the object is an extension incorporated in a lamp unit.
In accordance with another aspect of the present invention, a lamp unit to which a curved-surface printing method applicable to a member exposed to a high-temperature closed atmosphere is applied is provided. The lamp unit includes a bulb acting as a light source, a shade for intercepting a part of light emitted from the bulb, a reflector for reflecting light emitted from the bulb, a lamp body arranged behind the reflector, a lens arranged so as to sealingly cover a whole front surface of the lamp body, and an extension arranged between the lens and the lamp body and formed with an opening of substantially the same configuration as a front projected shape of a light emitting section of the lamp unit. The extension is formed on a portion thereof other than the opening with a surface decoration by curved-surface printing. The surface decoration is formed so as to cause fogging of 10% or less in a glass haze test.